A -β-lactamase-overproducing strain of Alcaligenes denitrificans subsp. xylosoxydans isolated from a case of meningitis

Abstract

A resistant (R) clinical isolate of Alcaligenes denitrificans subsp. xylosoxydans was recovered from CSF during treatment including piperacillin. This variant selected in vivo, and a second variant obtained in vitro from the initially susceptible (S) strain, both exhibited resistance to penicillins (ticarcillin, piperacillin) and cephalosporins, but remained susceptible to latamoxef and imipenem. Clavulanate (2 mg/L) restored the susceptibility of the two R-variants to penicillins. A β-lactamase of pI 9·5 was detected in both S and R strains, but overproduction was observed only in the in-vivo and in-vitro R-variants. This inducible β-lactamase hydrolysed benzylpenicillin, cephalothin and cephaloridine efficiently, but amoxycillin, ticarcillin and cefoperazone were only moderate substrates. The enzyme was inhibited by clavulanate, cloxacillin and imipenem (IC₅₀ between 3 and 9 mM), but not by aztreonam and chloride ions (1 mM). Resistance to β-lactams was not transferable by conjugation to Escherichia coli or Pseudomonas aeruginosa, and DNA agarose gel electrophoresis indicated that no plasmid was present in the isolates. Restriction patterns of chromosomal DNA isolated from the S and R isolates were similar after digestion by NotI and HindIII.